ANNIVERSARY ADDRESS OF THE PRESIDENT. 



81 



There is anotlier and totally different series of changes which 

 takes place in rocks, when, brought near to the surface by denudation, 

 they are exposed to the action of water, oxygen, carbonic acid, and 

 other atmospheric agents. The breaking-up of the alkaline silicates 

 and the deposition of secondary silica, the formation of the zeolites, 

 the epidotes, the chlorites, and the serpentines, the resolution of 

 crystallized minerals into isotropic mixtures, and the recrystalli- 

 zation of these in new forms, all offer problems of the highest 

 interest to the geologist. 



I may venture, in drawing these remarks to a close, to indicate 

 another point of analogy between the three Natural-History Sciences. 

 It is found in the circumstance that experimental verifications of 

 our conclusions are often difficult, if not actually impossible. 



We must be content to reason from the proved variability of 

 the existing forms of plants and animals as to the possibility of the 

 production in time of new species. And in the same way, with our 

 limited command of heat, pressure, and especially of time, we can 

 scarcely hope to originate the exact counterparts of all the various 

 minerals and rocks of our earth's crust. 



"We may nevertheless point with satisfaction to what, in spite of 

 such difficulty, has already been accomplished in this interesting field 

 of research. The honour of having pushed these researches to such 

 successful issues belongs chiefly to the chemists, mineralogists, and 

 geologists of France. To the labours of Senarmont, Daubree, and a 

 host of other workers we owe the artificial production of a very 

 large number of the minerals of our globe ; while the ingenious 

 experiments of Fouque and Michel Lev}* have resulted in the for- 

 mation of many rocks differing in no essential particulars from those 

 which have been produced by natural agencies. 



In the prosecution of his various researches the importance and 

 value of exact Mineralogical knowledge to the Geologist is becoming 

 every day more apparent. The temporary estrangement between the 

 cultivators of Mineralogy and Geology is now happily and for ever at 

 an end ; very heartily, indeed, do geologists recognize and welcome 

 the aid of their brethren the mineralogists. 



But if it be confessed that the benefits, past and prospective, 

 conferred on geological science by Mineralogy are vast and even 

 incalculable, it must also be admitted that the debt is amply repaid 

 by the beneficial influence which is being exercised in turn upon 

 Mineralogy by Geology. 



Some time ago a distinguished mineralogist asked me if I did not 



vol. xim. g 



